This invention relates generally to ac voltage regulators, and, more particularly, to switched ac voltage regulators that are highly efficient and provide a precise, continuously-variable voltage control.
Switching ac voltage regulators of this particular kind have been devised as a means of saving electrical power and thus reducing electric utility bills. Ac power supplied by utility companies is usually provided at a nominal voltage, plus or minus about 5 percent on a long term average. Short term deviations can be as great as plus or minus 10 percent of the nominal voltage.
Most electrical equipment is designed to operate as high as about 10 percent over the nominal voltage and as low as about 12 to 15 percent under the nominal voltage. The additional tolerance for low voltage is required to accommodate voltage drops that frequently occur in building wiring, between the utility entrance and the equipment.
If the electrical power supplied by the utility company is closely regulated to a constant voltage at the utility entrance, or at major distribution points within the user's facility, the voltage can be controlled at the minus 10 percent level, to reduce the power consumed. A voltage level of minus 7 or 8 percent could be used to provide some safety margin, if needed. This adjustment may be made by the individual user, to suit the specific need.
Many additional benefits are realized by operating electrical equipment at 7 to 10 percent below its nominally rated voltage. At such voltages, most electrical equipment operates at a lower temperature and has a longer lifetime.
To obtain the maximum benefit in energy savings, the ac voltage regulator for regulating the voltage to the desired, sub-nominal level, must be highly efficient and must have very fast response in correcting for dips in the input voltage so that the output voltage is not allowed to dip below the desired sub-nominal level for a time period that could cause improper operation of sensitive equipment making up the load. Given the present efficiency of commercial transformers and semiconductor switches, an efficiency rate of greater than 99 percent and a response time on the order of one millisecond should be achievable.
One prior switching ac voltage regulator of this particular kind includes a transformer with a secondary winding connected between the regulator's input and output terminals and a primary winding that is controlled to alternately carry a bucking current or a boosting current, such that the voltage and current supplied to the output terminal for delivery to a load are alternately decreased and increased, correspondingly. The duty cycle of the alternate switching between bucking and boosting current is controllably adjusted to provide a desired average (i.e., regulated) ac voltage output. Although such voltage regulators have proven generally effective in providing a continuously-variable, precisely-controlled regulated voltage, their efficiency is not believed to be as high as is practically possible. Further, additional circuitry such as snubber circuits and other protective circuits are required to ensure proper operation each time the regulator switches between a buck mode and a boost mode.
It should, therefore, be appreciated that there is a need for an improved, highly efficient switching ac voltage regulator that provides a precise, continuously-variable voltage control without the need for inefficient, protective circuitry for ensuring proper operation when the regulator switches between two alternative operating modes. The present invention fulfills this need.